Cylinder locks are generally comprised of a stationary housing and a rotatably mounted plug or cylinder and a plurality of pin tumblers of various lengths comprising an upper and lower segment which are pressed down from cavities provided in the housing by springs to engage with holes in the cylinder, thus preventing the latter from rotating. Upon insertion of a properly cut key each pin tumbler is raised so that the top of the lower segment is flush with the top of the cylinder, allowing the segments to separate and the cylinder to be turned in the housing.
However, to date all such cylinder locks employ pin tumblers which are laterally spaced along a single line running parallel with the axis of the cylinder and may be raised only by using a generally long, flat key provided with a plurality of irregular teeth and alternating indentations along a single edge thereof. For this reason, the number of pin tumblers which may be used and the variations of alternative heights of said pin tumblers within the cylinder are extremely limited.
Another disadvantage of such cylinder locks which can generally accommodate only from four to six laterally spaced pin tumblers is that due to the lateral arrangement of the several pin tumblers, the lock becomes very susceptible to unauthorized "picking" or opening without the use of the proper key.
In addition, the flat key can be placed in the slot-like opening of the cylinder in only one way, which can be very frustrating for children and especially irritating when trying to unlock a door in an unlighted or poorly lit area where the exact position of the slot is not readily ascertainable.
Furthermore, as the flat key can be inserted only in one position, there is much wear on the toothed face of the key, causing the lock to "stick" and generally become harder to open as time goes on.
Also, the flat key is very susceptible to breakage after being inserted into the cylinder, often necessitating the complete replacement of the entire lock.
Another disadvantage of the flat key is that there are many sharp edges which may prove hazardous to children and which occasionally cause tears in pockets and clothing.